The present invention relates to the apparatus and process for making an expanded variety of tapered tube sections from formed sheet metal and completed by welding-sizing apparatus of this invention. More specifically, the present invention is a group of apparatuses and processes with intent for welding by electrical resistance method and rolling the welded tube section through sizing apparatus with no means of mandrel or any other internal tool.
It is known in the traditional technology to manufacture tapered tube sections by forming a metal blank which is cut to trapezoidal geometry' out of plate or sheet metal into a conical tube shape and then welding the opposite edges (long side) of the formed blank by an electrical welding method well known as a high frequency welding. However, none of the known methods or apparatus is practical and efficient in operation and pose limitations in terms of tapered tube products geometry such as lengths, diameters or shapes which are to be manufactured. The number of the known apparatuses for manufacturing tapered tube sections in reality is represented by only one particular process. For example, forming, welding or finishing (rolling, burnishing) and some accessories to each one individually. Such disconnects make those apparatuses limited by application.
One example of such prior art practice is found in U.S. Pat. No. 6,629,632 issued to R. Jack and J. Brook and is shown in FIGS. 17 and 18. This invention consists of a “means for applying inwardly directed radial forces to the shaft at a plurality of discrete points on the surface of the shaft [comprising] a plurality of pressure rollers defining an opening through which the shaft is fed, and means for varying the positions of the rollers[.]” One disadvantage of this apparatus and method is the limitation of cross sections to be welded in stable conditions. In other words, when space between rollers grows, material of the tapered tube section will be deformed between rollers under pressure that are intended to be used mostly to create welding fusion. The tapered tube section will be distorted, with increasing distortion toward the larger diameter of the tapered section and exhibit weld defects as well. A second disadvantage of U.S. Pat. No. 6,629,632 is the absence of a secondary operation such as finishing that is required to fix shape discrepancy of the tapered tube section.
Another example of such prior art practice is found in U.S. Pat. No. 3,648,008 issued to T. Kawato et al. Shown is welding apparatus in which “a preformed tapered tube is inserted between miniaturized forming rollers having cam faces . . . and as said tube is drawn . . . the welding is performed on a longitudinal aligned edges of the tube so as to make desired products by means of the comparatively small high-frequency welding apparatus.” This type of roller is known as a “sleep roll” and ensures the tapered tube will be welded, but may not deliver desired shape, size or finishing process at the end.
The next example of such prior art practice is found in U.S. Pat. No. 3,802,239 issued to Karmann et al. This patent discloses an apparatus and process “for forming an elongated tapered tube for use as light poles and the like, the machine comprising means for supporting a flat, trapezoidal sheet of metal in a horizontal position, an elongated mandrel having the shape of the tube to be formed held down along the longitudinal axis of the sheet, a pair of forming elements mounted along each side and below the sheet with power means for raising the formers upwardly and moving them inwardly toward each other whereby to form the sheet about the mandrel, means for flattening the edges of the sheet such that they are contiguous for welding purposes, and means for removing the formed tube from the machine as another sheet is brought into the machine and placed on the supporting means.” This prior art was proposed to finish welded tapered tube by a series of rollers that roll on the outside diameter of tapered lube with a mandrel inside. This type of finishing process required an internal tool along with extra steps to insert the mandrel into the tapered tube and mandrel extraction at the end of the operation. This process will require significant modification to be operated in line with welding apparatus. In addition, because of stretch, the tapered tube will increase in length while the thickness of the tube will decrease.
An additional example of a sizing or finishing practice is found in U.S. Pat. No. 7,296,450 issued to Y. Kuroda. Shown is a “production apparatus for a tapered steel pipe which holds the two ends of the steel pipe by shafts on carriers and moves it in the axial direction while rotating it to draw it to a taper by an intermediate working roll, wherein the shaft of the working roll is inclined 20 to 40 degrees with respect to the axis of the steel pipe and a roll caliber of the working roll is made an outwardly curved surface with little difference in roll peripheral speed; the face plate for mounting the working roll is positioned and supported with respect to the body by a hinge mechanism and is fastened to the body by fastening members; and the bearing of the working roll at the side close to the steel pipe is made smaller than the bearing at the side far from the steel pipe and the two bearings are connected by a tie-rod.” The process has a great deal of limitations as far as tapered tube diameter, shape and length and is extremely dependent upon the wall thickness of the straight tube.
Metal tapered tube product is well known and used as a utility supporting structure in infrastructure, communications and street lighting.